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Single-Molecule Imaging Reveals How Mre11-Rad50-Nbs1 Initiates DNA Break Repair

Logan R Myler1, Ignacio F Gallardo2, Michael M Soniat2

  • 1Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA; Howard Hughes Medical Institute, The University of Texas at Austin, Austin, TX 78712, USA; Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA.

Molecular Cell
|September 5, 2017
PubMed

Insights

The Mre11-Rad50-Nbs1 (MRN) complex finds DNA breaks using facilitated diffusion and removes blocking proteins like Ku. MRN then recruits and stabilizes Exonuclease 1 (Exo1) for DNA repair via homologous recombination.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • DNA double-strand breaks (DSBs) threaten genome stability.
  • The Mre11-Rad50-Nbs1 (MRN) and Ku70-Ku80 (Ku) complexes manage distinct DSB repair pathways.
  • The interaction between MRN and Ku at DSBs is not fully understood.

Purpose of the Study:

  • To elucidate the mechanism of MRN complex action at DNA double-strand breaks.
  • To understand the interplay between MRN and Ku in DNA repair.
  • To investigate how MRN facilitates homologous recombination on nucleosome-coated DNA.

Main Methods:

  • High-throughput single-molecule microscopy.
  • Analysis of DNA end binding and nucleolytic activities.
  • Investigating the role of Rad50, Mre11, and Exo1 in DNA resection.

Main Results:

  • MRN utilizes one-dimensional facilitated diffusion to locate DNA ends, even on nucleosome-covered DNA.
  • Mre11 is crucial for DNA end recognition and nuclease activity, enabling MRN to displace Ku.
  • MRN acts as a processivity factor for Exonuclease 1 (Exo1) in the presence of Replication Protein A (RPA), promoting long-range resection.

Conclusions:

  • MRN complex employs facilitated diffusion for DNA end searching and Ku removal via Mre11-dependent nucleolysis.
  • MRN recruits and stabilizes Exo1 for DNA resection, facilitating homologous recombination repair on challenging DNA substrates.
Keywords:
DNA repairKuMRNdouble-strand breakresectionresectosomesingle-molecule

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